The valve insert part is usually inserted into the base part by screwing. The valve insert part is screwed with an external thread into an internal thread in the bore of the base part. This has proven difficult, the reason being that although only a small thread pitch has to be provided for the good seal required between the base part and the valve insert part, this thread pitch requires precise screwing of the valve insert part into the base part. This precise screwing cannot be provided with certainty by patients who are expected to carry out this screwing movement with poor visual contact or indeed with no visual contact. Therefore, this screwing is sometimes not possible at all, or it is sometimes possible only with great effort or with the help of a third person.
WO 2007/001745 A2 discloses a threadless valve arrangement in which the valve insert part can be inserted into the base part with the aid of latching elements. The valve insert part in this case has a circular cylindrical stub, which carries an O-ring as seal. This stub can be inserted with a matching fit into the circular cylindrical bore of the base part. On a flange end directed away from the stub, the valve insert part has latching arms designed as two-arm levers which, at their end pointing toward the stub, have a latching rib able to grip behind a locking projection of the base part radially from outside. The movement of the latching arms into the latching position is supported by a helical spring pushed onto a latching pin. At the end of the latching arms directed away from the locking rib, there are actuating projections behind which fingers can be placed in order to press the upper ends of the latching arms radially inward, and thus press the locking ribs radially outward, and release the latching connection between valve insert part and base part, such that the valve insert part can be withdrawn from the base part.
The known valve arrangement permits considerable easier actuation of the valve arrangement for the removal of the valve insert part and for the subsequent insertion thereof into the base part. The valve insert part is in this case complicated to assemble because of the required assembling of the rotation axis, designed as a metal pin, of the latching arms onto which the helical spring designed to function as rotation spring has to be pushed and has to be positioned in a correctly tensioned state of the coil ends relative to the housing of the valve insert part, on the one hand, and to the actuation arm, on the other hand.